Biology · Principles of Inheritance and Variation · NEET
'Hetero' means different and 'gamete' means sex cell. So a heterogametic sex makes TWO different types of gametes. In humans the male makes sperm carrying an X and sperm carrying a Y, so the male is heterogametic. A 'homogametic' sex makes only ONE type of gamete (all the same). The human female makes only X-eggs, so she is homogametic.
In male heterogamety the MALE is the one that makes two different gametes. This happens in the XX-XY type (humans, Drosophila) and the XX-XO type (grasshopper). In both, the female makes only one type of gamete (all carry X), and the male makes two types. NEET loves the line: female is homogametic (XX), male is heterogametic.
Grasshopper is MALE heterogamety. It uses the XX-XO type: the male has only one X (written as XO, the O means no partner), so he makes two kinds of sperm — some carry X and some carry no sex chromosome. The female has two X (XX) and makes only one kind of egg. NEET 2023 tested exactly this: 'It is female heterogamety' was marked WRONG.
Yes. Humans use XX-XY, which is male heterogamety. The female is XX and makes only X-eggs (homogametic). The male is XY and makes two types of sperm: half carry X, half carry Y (heterogametic). The Y-sperm decides a boy, so the father decides the baby's sex, not the mother.
In birds the FEMALE is heterogametic. Birds use the ZW-ZZ type. The male is ZZ (makes one type of gamete = homogametic) and the FEMALE is ZW (makes two types = heterogametic). We use letters Z and W instead of X and Y just to show it is a different system where the female carries the odd chromosome.
Look at the two sex chromosomes. If they are the SAME (XX or ZZ) that sex is homogametic — one gamete type. If they are DIFFERENT or one is missing (XY, XO, ZW) that sex is heterogametic — two gamete types. Then name the system after whichever sex is heterogametic: male-hetero (XY/XO) or female-hetero (ZW).
Yes. In grasshopper (XO), the male has only one X and the female has two X. So the male has ONE chromosome fewer than the female. NEET 2026 used this: members with 23 chromosomes are MALES and members with 24 chromosomes are FEMALES.
Match Column I with Column II: (a) XX-XO method (b) XX-XY method (c) Karyotype-45 (d) ZW-ZZ method; (i) Turner's syndrome (ii) Female heterogametic (iii) Grasshopper (iv) Female homogametic. Select the correct option.
Select the correct statement/s about sex determination in Grasshopper. A. It is an example of female heterogamety. B. Male produces two different types of gametes either with or without X chromosome. C. Total chromosome number is same in both sexes. D. All eggs bear an additional X chromosome besides the autosomes.
XO type of sex determination can be found in
Try the real previous-year questions from this chapter — each with the answer and a full solution.
In male heterogamety the MALE makes two gamete types (XY humans, XO grasshopper); in female heterogamety the FEMALE makes two gamete types (ZW birds).
Birds, butterflies and moths show female heterogamety (ZW-ZZ type). Here the female is ZW and heterogametic, while the male is ZZ and homogametic.
XX-XY is MALE heterogamety. The female is XX (homogametic, one egg type) and the male is XY (heterogametic, two sperm types). Humans and Drosophila use this.
To avoid confusion. In birds the odd chromosome sits in the female, which is the opposite of humans. Using new letters (ZW female, ZZ male) clearly shows the female is the heterogametic one.
Yes. The heterogametic sex decides the offspring's sex, because it supplies the two different gametes. In humans the father (XY) decides; in birds the mother (ZW) decides.
